FIG. 1 (Prior Art) is a diagram of a broadcast television system 100, including a broadcast headend 102 connected via a broadcast network to a number of receivers 104. The broadcast network can be wired (e.g., a cable system), wireless, or a combination of the two. Broadcast headend 102 optionally includes a server (not shown) maintained by a broadcaster to store digital information for broadcast. Similar servers can be maintained by other entities and can be made available to receivers 104 via a separate broadcast medium or a direct connection, such as via a modem or satellite connection.
Each receiver 104 has a corresponding display, often a conventional television set 106. Each receiver 104 connects to its respective television set 106 via an audio-video link 110. Users control receivers 104 via a user-input device, typically an infrared remote control 108 or a control panel (not shown) on their respective receivers 104.
FIG. 2 is a block diagram of a typical digital receiver 104. A digital processor 202 is the “brains” of receiver 104. Processor 202 typically includes a number of components, including a central processing unit (CPU) and memory, for example. Processor 202 has many variations, depending primarily upon the desired functionality. The internal workings of processor 202 are outside the scope of this disclosure. Those interested in additional information about a typical set-top box may refer to U.S. Pat. No. 5,940,074 entitled “Remote Upgrade of Software Over a Network,” which is incorporated herein by reference.
An infrared interface 214 receives instructions from an infrared remote control. A simple display 216 provides the user with a visual indication of e.g. whether receiver 104 is powered on and, if so, the channel to which broadcast interface circuit 204 is tuned. Processor 202 may present additional information to the user via the attached video display. Receiver 104 optionally includes a modem 210 for connecting to the Internet and some form of local mass storage 212, such as a disk drive.
Processor 202 receives data derived from broadcast video signals by a broadcast-interface circuit 204. Broadcast interface circuitry 204 includes one or more tuners that discriminate one signal from among a number of incoming broadcast signals and removes the associated carrier frequency. Interface circuitry 204 digitizes the resulting audio and video data and conveys the resulting digital information to processor 202.
Processor 202 processes the information from interface circuit 204 as necessary to present appropriately formatted audio and video data to an audio digital-to-analog converter 206 and a video encoder 208, respectively. The resulting signals are then conveyed to television 106 or some other display.
Receivers 104 receive periodic updates from broadcast headend 102. For example, a broadcaster may send each receiver 104 an updated program guide or a software update. Some components of receiver 104 must be powered up to receive broadcast content; unfortunately, this means much of the receiver is always powered up, even when the user is not watching television, and has therefore turned off receiver 104. In the depicted example, a power supply 220 provides power continuously at least to broadcast interface circuit 204, processor 202, and IR interface 214. In point of fact, turning “off” common receivers similar to the ones described here typically removes power only from user display 216: turning off the user display comforts frugal consumers, but saves little power.
Leaving most of receiver 104 on at all times wastes power and money. To make matters worse, receivers of the type described herein are proliferating, and are in the process contributing to an epidemic of power shortages. There is clearly a need for more power-efficient broadcast receivers.